An example of an antenna apparatus housed in a casing is disclosed in U.S. Pat. No. 6,498,589 patented on Dec. 24, 2002. The antenna apparatus disclosed therein includes a main body having a generally octagonal shape in plan, and a lid or cover closing an opening in the main body. Four Yagi antennas are arranged in the main body. First two of the four Yagi antennas are aligned on a first imaginary straight line passing through the main body, and exhibit directivities oriented in mutually opposite directions along the first imaginary straight line. The remaining, second two Yagi antennas are aligned on a second imaginary straight line extending orthogonal to the first imaginary straight line and exhibit directivities oriented in mutually opposite directions along the second imaginary straight line. The second two Yagi antennas are disposed in a plane at a level vertically deviated from the level of the plane in which the first two Yagi antennas are disposed. Each Yagi antenna includes antenna elements, namely, a radiator, a reflector and a director, and is disposed within the main body.
The prior art antenna apparatus includes four Yagi antennas so as to have directivities oriented in different four directions, and each Yagi antenna includes a plurality of elements, such as a radiator, a reflector and a director. Four of such Yagi antennas formed of many components must be housed in a single casing, and, therefore, the assembling efficiency is low. In addition, two Yagi antennas must be placed in one plane, while remaining two must be placed in a different plane, which further degrades the assembling efficiency.
An object of the present invention is to provide an antenna apparatus which can be assembled with improved efficiency.